An elevator typically comprises an elevator car movable in the hoistway. The elevator further comprises a rotatable traction member, such as a traction wheel, engaging suspension ropes connected to the elevator car. The suspension ropes are typically engaged frictionally by the traction wheel. The suspension ropes pass around the rotatable traction member and suspend at least the elevator car, but usually also a counterweight. For controlling rotation of the rotatable traction member, the elevator comprises a drive machinery, which typically comprises a motor for rotating the rotatable traction member, a control unit for controlling the motor, as well as a brake for braking rotation of said rotatable traction member. Force for moving the car and counterweight is transmitted from the motor to the car via the rotatable traction member and the ropes, whereby movement of the elevator car can be controlled by controlling rotation of the rotatable traction member.
In the event that the car needs to be stopped immediately, a so called emergency stopping is initiated. In the emergency stopping the car is brought into a sudden stop, typically by braking rotation of the traction wheel. A drawback of the known solutions is that an aggressive braking of the traction wheel causes the risk that the engagement between the ropes and the traction wheel is lost. Occurrence of slipping between the ropes and the traction wheel would slow down the progress of the emergency stopping.
Conventionally, elevator ropes are made of steel wires, thereby having a surface made of steel. In prior art, there are also such ropes which have their load bearing member(s) coated with material comprising polymer. By polymer based coating, it is for example possible to adjust, usually aiming to increase, the power transmitting ability over the frictional engagement. The load bearing members can also be protected by the coating. Furthermore, the coating may be used for binding several load bearing members together. In prior art, there are also traction wheels having a traction surface made of material comprising polymer. It has been noted that risk of occurrence of slipping between the ropes and the traction wheel is increased if one or both of the rope and the traction wheel comprises a surface made of material comprising polymer and the temperature of the material comprising polymer rises excessively. In case of high temperature, polymer materials typically melt or at least substantially change their friction properties in temperatures 140-250 degrees centigrade. In case of high temperature, the friction coefficient becomes lower and tensioned rope may start more easily to slide along the traction sheave. This kind of slip with abnormally low friction coefficient has to be prevented during emergency stops, but also in uncontrolled movement situations, i.e. in situations where the car is stopped at a landing with open doors.